Many removable data storage devices are provided with a casing to protect the data storage media in the device from contamination and physical damage. Typically, the casing includes openings therein to allow access to the data storage media contained in the removable data storage device. The removable data storage device also often includes a shutter for covering the openings when the device is not in use, thereby offering some protection to the data storage media.
One common type of removable data storage devices comprise discs of polyester resin or the like having a magnetic layer on each side thereof forming the media on which information is recorded by a magnetic head. A magnetic data storage disc with a diameter of 31/2 inches (8.9 cm) or less is known as a micro-floppy disc and will be referred to so herein. Generally, the micro-floppy disc is accommodated in a hard casing to form a removable data storage device.
The casing enclosing the media of a micro-floppy disc includes two oppositely positioned head window openings through which the media is exposed to allow the reading and writing of data on the media. To protect the data storage media when the disc is not positioned in a disc drive, a spring-biased shutter is provided that covers the head window openings. The design of the micro-floppy disc is subject to American National Standards Institute (ANSI) standard x3.171-1989 and equivalents (such as ISO/IEC 9529-1:1989 and European Computer Manufacturers Association ECMA/TC 19/87/21) to allow interchangeable use of micro-floppy discs in different micro-floppy disc drives, both of which may be manufactured by many different companies. As a result, the dimensions of the shutters for such discs do not typically vary significantly between manufacturers.
Shutters are typically manufactured of stainless steel, aluminum, or plastic. Although shutters manufactured from stainless steel are particularly resistant to corrosion and possess sufficient strength to resist permanent deformation during normal use, they are typically more expensive than, for example, aluminum or plastic shutters. As a result, plastic and aluminum shutters are more prevalent.
Aluminum shutters are typically anodized to enhance their stiffness and ability to resist corrosion. Although anodizing increases the stiffness of the shutters, even anodized aluminum shutters do not have the stiffness of stainless steel shutters. In addition, the anodized aluminum shutters will permanently deform sooner, i.e., with less deflection, than a stainless steel shutter with the same thickness. The low stiffness and permanent deformation can make aluminum shutters more susceptible to becoming lodged in a disc drive if the sides of the shutter become permanently deformed. Such deformation, where the sides of the shutter are splayed outward, can make removal of the micro-floppy disc from the drive difficult (with the possibility of damage to the disc and/or disc drive during removal of the disc).
Another problem with anodized aluminum shutters is that although the anodizing increases the stiffness of the aluminum, the anodizing can crack at the bends used to form the shutter as well as at the edges of the shutter (if it is stamped from a coil of anodized aluminum). The areas where the anodizing is cracked do not exhibit the enhanced stiffniess of the anodized aluminum, but rather exhibit the lower stiffness of the underlying aluminum alone. As a result, the shutter is even more prone to permanent deformation and, in some cases, fracture along the bends formed in the aluminum shutter.
Although the use of plated steel has been discussed for shutters on micro-floppy discs, it is not typically used because of the susceptibility of plated steels to corrode at any voids in the plating, including cracks that develop when the shutters are formed, i.e., bent, to the desired shape, as well as at sheared edges. In addition, the plated steel shutters are also susceptible to scratches and other surface defects during transit and handling of the shutters as they are jostled against each other or storage trays. Although the cracks and other surface defects formed in the shutters are small, they provide the starting point for corrosion by exposing a portion of the underlying steel. In addition to degrading the aesthetic appearance of the micro-floppy disc (or other removable data storage device), the corrosion can weaken the shutter, thereby increasing the chance for permanent deformation of the shutter.